Nardoa arabica, Voigt et al., 2017

Van, Rob W. M. & De, Nicole J., 2018, Calcareous sponges of the Western Indian Ocean and Red Sea, Zootaxa 4426 (1), pp. 1-160 : 55-59

Ernstia arabica Voigt et al., 2017

Figures 28a–c , 29a–c , 30a–e

Ernstia arabica Voigt et al., 2017: 9 , figs 5a–e.

Material examined. ZMA Por. 13640, Israel, Coral Garden , Gulf of Aqaba, depth 1.5 m, scuba, coll. M. Wunsch, field nr. AQ140, 15 July 1998 ; ZMA Por. 13642, Egypt, Ras Mohammed, Shark Observatory , depth 15 m, scuba, coll. M. Wunsch, field nr. RM 222, 23 July 1998 .

Description. There are two, rather different specimens from the Gulf of Aqaba, which are assumed to be members of this species. Because of the differences we describe them separately. Cormus of ZMA Por. 13640 ( Fig. 28a ) small yellow cushions connected by thinner stolon-like parts, structure compact made up of tightly anastomosed thin tubuli ( Fig. 28b ). Oscules centrally located on the cushions and slightly elevated. Lateral size of cormus up to 2.5 x 1 cm, thickness about 5–8 mm. ZMA Por. 13642 is a flatly encrusting cormus ( Fig. 30a ) consisting of tightly anastomosed thin tubuli. Pale yellow in life, dirty white in alcohol. Several broader tubuli lead to a few wide oscules slightly raised above the cormus. Lateral size 5 x 4 cm. Constency soft.

Aquiferous system. Asconoid.

Skeleton. ( Figs 28b–e ) Walls of tubuli in both specimens are thin ( Fig. 28c ), consisting of one–two spicule layers ( Figs 28d , 30b ) with a mixture of tri- and tetractines; the apical actines of the latter are protruding into the tubule lumina ( Fig. 28c ) forming a dense palisade ( Fig. 28e ). Consistency firm.

Spicules. ( Figs 29a–c , 30c–e ) Triactines and tetractines, the latter present in clearly larger numbers. No distinct trichoxeas were found.

Triactines equiradiate and equiangular, with conical actines, some verging toward tripod-shape.

Actine sizes of ZMA Por. 13640 ( Fig. 29a ) measure 89– 98 –105 x 9 – 11.2 –13 µm.

Actine sizes of ZMA Por. 13642 ( Figs 30c ) measure 102– 125 –165 x 11 – 16.4 –26 µm.

Tetractines of similar shape and size to the triactines, equiangular, with conical actines.

Actines of the basal triradiate system in ZMA Por. 13640 ( Figs 29b ) measure 87– 94 – 99 x 9 – 10.3 –12 µm, apical actines ( Fig. 30c ) smooth, straight, 66– 76 – 91 x 5 – 6.6 –8 µm.

Actines of the basal triadiate system in ZMA Por. 13642 measure ( Figs 30d ) 67– 127 –182 x 9 – 15.2 –27 µm; apical actines ( Fig. 30e ) shorter, thinner and sharper, 23– 38 – 59 x 3 – 5.7 –11 µm.

Distribution and ecology. Israelian Red Sea, Saudi Arabian and Egyptian Red Sea ( Voigt et al. 2017), down to 15 m.

Remarks. The present specimens closely resemble the type in most aspects, except for the absence of trichoxeas. These were also not consistently present in the type material ( Voigt et al. 2017). A small further difference is the length of the apical actine of the tetractines, which has a greater range in the type material (up to 156 µm). The two present specimens differ subtly in the habitus and the smaller-thinner vs. the larger and more robust spicules. Voigt et al. (2017) described and measured the spicules of specimens from the Northern and Southern Red Sea and found triactines and tetractines having actine lengths between 38 and 116 µm, and apical actines between 56 and 156 µm, while our own specimens have these data respectively 67–182 µm and 23–91 µm.

Unfortunately, we were unable to obtain partial 28S rRNA sequences for these specimens. Below we compare E. arabica with Western Indian Ocean specimens identified as the closely related Ernstia naturalis Van Soest & De Voogd, 2015.

Figures

FIGURE 28. Ernstia arabica Voigt et al. 2017, ZMA Por. 13640, from the Gulf of Aqaba, a, habitus in situ (photo M. Wunsch), b–e, SEM images of sections of the cormus, b, overall section showing tightly anastomosed tubuli, c, cross section of tubuli showing apical actines of tetractines protruding in the tubar lumen, d, cross section of the surface region, e, detail of tubar lumen and protruding apical actines.

FIGURE 29. Ernstia arabica Voigt et al. 2017, ZMA Por. 13640, from the Gulf of Aqaba, SEM images of the spicules, a, triactine, b, tetractines, c, detail of apical actine of tetractine.

FIGURE 30. Ernstia arabica Voigt et al. 2017, ZMA Por. 13642, from Northern Red Sea, Egypt, Ras Mohammed, a, habitus in situ on the reef (photo M. Wunsch), b, light microscopic image of a detail of the cormus, c–e, SEM images of the spicules, c, triactines, d, tetractines, e, detail of apical actine of tetractine.